1. Field of the Invention
The present invention relates to an image forming apparatus configured to form a toner image on a recording sheet via the charging, exposure, development, and transfer processes of an electrophotographic method.
2. Description of the Related Art
Conventionally, there is a tandem type image forming apparatus which includes four photosensitive drums for yellow, magenta, cyan, and black colors and an intermediate transfer belt onto which a toner image is transferred from each of the photosensitive drums. As discussed in Japanese Patent Application Laid-Open No. 2010-145556, when forming an image, the conventional tandem type image forming apparatus controls the intermediate transfer belt to abut onto the four photosensitive drums in a color print mode and to separate from the three photosensitive drums excluding the drum for the black color in a monochrome print mode.
The abutment operation of the intermediate transfer belt against the photosensitive drum is performed by moving a primary transfer roller closer to the photosensitive drum. The separation operation of the intermediate transfer belt from the photosensitive drum is performed by moving the primary transfer roller away from the photosensitive drum.
In the ideal state, the intermediate transfer belt is conveyed without moving in the direction perpendicular to the movement direction of the intermediate transfer belt (i.e., in the width direction). However, it is known that the intermediate transfer belt tends to move in the width direction due to various factors, such as the tilt of a roller that supports the intermediate transfer belt, a tension difference between the left and the right sides of the intermediate transfer belt, and a difference in the external load. When the intermediate transfer belt moves in the width direction, meandering may occur. As a technique for correcting such meandering of the intermediate transfer belt, Japanese Patent Application Laid-Open No. 2009-282196 discusses a technique that corrects the meandering by tilting a steering roller.
However, if the intermediate transfer belt is attached to the photosensitive drum or the intermediate transfer belt is separated from the photosensitive drum when the intermediate transfer belt is conveyed in a stable manner, the stability of the conveyance of the intermediate transfer belt may be affected. This is because, the abutment operation or the separation operation may change a pressing force from the photosensitive drum and the primary transfer roller and a position that receives the pressing force, which causes a change in the angle of the tilt of the steering roller that can realize the stable conveyance of the intermediate transfer belt. Thus, when the abutment operation or the separation operation is performed, a large meandering of the intermediate transfer belt temporarily occurs.
Such a meandering occurs not only when the primary transfer roller is involved. In other words, it is an issue that occurs when a rotatable member is involved in the abutment and separation operation with respect to the intermediate transfer belt. Further, the issue occurs not only with the intermediate transfer belt but also with other types of belts, such as a conveyance belt that conveys a recording sheet, having a rotatable member involved in the abutment and separation operation.